Method and apparatus for producing a stereo image by electron microscopy

ABSTRACT

For producing a stereo image, for example of a crystalline object, by electron beam microscopy, any chosen surface area of the object is rotated about a central axis defined by the direction of the electron beam. The amount of rotation is such that after a subsequent tilting of the object about a second axis intersecting the central axis, the image intensity of the surface area is the same in the starting position as in the end position of the tilting displacement. Respective individual pictures are taken in these two object positions.

United States Patent [56] References Cited UNITED STATES PATENTS2,360,677 10/1944 Hillier 250/495 A 3,086,112 4/1963 Riecke 250/495 B3,435,210 3/1969 Valdre 250/495 B Primary Examiner-James W. LawrenceAssistant ExaminerD. C. Nelms Attorneys-Curt M. Avery, Arthur E.Wilfond, Herbert L.

Lerner and Daniel J. Tick ABSTRACT: For producing a stereo image, forexample of a crystalline object, by electron beam microscopy, any chosensurface area of the object is rotated about a central axis defined bythe direction of the electron beam. The amount of rotation is. such thatafter a subsequent tilting of the object about a second axisintersecting the central axis, the image intensity of the surface areais the same in the starting position as in the end position of thetilting displacement. Respective individual pictures are taken in thesetwo object positions.

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mm P mm, a l 3 A2 llilmhj W 0} MA Xm PATENTED UECZI X97! SHEET 3 BF 3METHOD AND APPARATUS FOR PRODUCING A STEREO IMAGE BY ELECTRON MICROSCOPYOur invention relates to a method for producing a stereo image whoseindividual images, for example of a crystalline object, are produced bymeans of electron microscopy.

It is known that devices for producing stereo image pairs of crystalspecimens by scanning electron microscopes must be equipped with deviceswhich permit displacing each point of the specimen with respect to itsdistance from the electron beam, and which also permit tilting thespecimen surface about an axis which is nearly or preciselyperpendicular to the electron beam direction. It is further known thatpairs of stereo images to be viewed with known optical equipment, can becombined to a stereo image only if the stereo angle remains limited inaccordance with physiological optics, for example the Liischer-parallaxcondition. The production of stereo images further requires that theimage brightnesses of the object surfaces in the two individual imagesbe not, or only slightly, different from each other. The change in imagebrightness when tilting the object is due to the fact that the number ofsecondary electrons released by the primary electron beam out of aspecimen surface, and consequently the image brightness of the objectsurface, greatly depends upon the inclination angle of the surfacenormal of the object relative to the direction of the primary electronbeam. It may happen, therefore, that a stereo effect of interestingobject structures cannot, or only very deficiently, be attained if atthe mutually corresponding localities of the individual images produced,the image intensities differ so greatly from each other that no genuinestereo effect will result. For the same reason, it may be difficult tomeasure the local object height.

It is an object of our invention to provide a method and means for theproduction of stereo images by electron microscopy which minimize orvirtually eliminate the abovementioned difficulties. More specifically,it is an object of the invention to readily afford producingelectron-optical stereo images which secures substantial constancy ofthe image brightness with respect to given object surfaces in the twoindividual images of a stereo pair.

According to our invention, we first rotate the chosen surface area orface of the object about a central axis defined by the direction of theelectron beam, whereafter we tilt the object about a second axisintersecting the central axis, the tilting being in an amountcorresponding to the stereo angle; and the rotation about the centralaxis being such that the image brightness of the surface issubstantially the same in the starting position and in the end positionrespectively of the tilting displacement. The individual pictures of thestereo pair are taken as the object is in these two positionsrespectively.

Preferably, the cented axis and the second axis are perpendicular toeach other, and the point of intersection is situated within the objector specimen.

According to another feature of our invention, a third axis may beprovided which passes through the intersection of the first and secondaxes and which extends perpendicularly or at a different angle to eachof these two axes, the specimen being rotatable about the third axis formaintaining a given surface brightness intensity of the object.

According to a further, alternative method of the invention, any chosensurface of the object is rotated about an axis which is noncoincidentwith the beam direction; and adjustable so as to be parallel to, oridentical with, the normal direction of the surface (i.e., the directionperpendicular to the surface), the amount of rotation, constituting thestereo angle, being dependent upon the angle between the adjustable axisand the central axis defined by the beam direction.

As a consequence of the object movements performed in accordance withthe above-described method of the invention, noninteresting object facesor surface areas can be uniformly suppressed as regards their brightnessintensity on the corresponding localities of the stereo image pair, thusmore clearly imaging and emphasizing the other structural features ofthe object. This is tantamount to having the possibility of varyingand/or improving the image contrasts. For example, the intensity of aplanar crystal surface can be uniformly suppressed for more clearlyimaging any individual small etch pits located on the surface.

The invention will be further elucidated with reference to theaccompanying drawing in which:

FIG. 1 is an explanatory diagram;

FIG. 2 is a schematically perspective view of apparatus embodying theinvention by way of example; and

FIG. 3 is a schematically perspective view of another apparatus alsoembodying the invention by way of example.

The diagram shown in HO. 1 serves to permit a comparison of the methodaccording to the invention with those heretofore available. Theperspective representation indicates various axes. Among these is theZ-axis (central axis) shown with an arrowhead opposed to the directionof the primary beam of electrons. Also apparent is an axial direction Xwhich is perpendicular to the primary electron-beam direction (Z-direction) and about which the specimen surface, in the heretoforecustomary manner, was tilted in opposition to the beam direction 1 aboutthe angles 1 in order to first obtain a given image brightness of thesurface, and thereafter is tilted through the stereo angle MD to theangular position 1 Also indicated in FIG. 1 is an axis Y which isassumed to be perpendicular to the X-axis and to the Z-axis, although itmay also intersect these two axes at a different angle. The Z-, Y- andX- axes are shown to intersect in a single point P although this is notan indispensable requirement. Further represented is a spherical surface0 about the common intersection P of the three axes with latitudecircles A and B concentric to the X- direction and Y-directionrespectively.

For simplification, assume that the surface structure of the specimen iscomposed of three areas conjointly forming a triple-edged pyramidrepresented in central projection. The surface normal (not shown) passesthrough the intersection point P of the axes and intersects the surface0 of the sphere at C, D and E.

In the conventional method for producing a stereo image, the twoindividual images of the stereo pair differ from each other in that thetilting angle 1 denoting the angular displacement about the X-axis,after first taking a picture at an angle D is changed by the stereoangle Ad to assume the angular position 1 this being represented atpoint C. Relative to this tilting displacement, the I -tilting axisperpendicular to the cented axis Z is designated as the X-axis. Due tothe tilting displacement, the surface normal directions passing throughC, D, E change to directions passing through C, D, E respectively. TheY-direction which is assumed to be fixed with the specimen, changesalong the latitude circles A to the Y- direction. In the following, thepoints C, C, C, C,, C,, D, D, E, E where the surface normal directionspassing through the sphere center point intersect the surface 0 of thesphere, are used to denote the surface normal directions as well as thesurfaces C, D and E themselves.

As a consequence of the tilting displacement, the corresponding surfacesC and C, D and D, E and E in the two individual pictures are imaged inrespectively different sizes and also with different image brightnesses.Thus, for example, it may happen that the increased inclination of thesurfaces C and E will result in a higher image intensity relative to Cand E, whereas the brightness at the surface D in the second picture Dis reduced. For similar reasons, an inversion in contrast of the areabrightness may take place and may weaken or obviate the stereo effect.

The method according to the invention minimizes or eliminates thesedifficulties at least with respect to any surface area of interest tothe observer. In lieu of the additional tilting about the X-axis by theangle A l we provide for other displacing movements of the specimen.That is, we provide for a rotary displacement about the central axis andtilting movement about the Y-axis which extends at an angle, for exampleperpendicularly, to the Z-beam direction (central axis) as well as tothe X-axis. For explaining the method steps, let it be assumed that thesurface area denoted by C is the one which,

with respect to image structure, intensity and characteristiclimitation, is of particular importance. This arbitrarily selectedsurface area C is inclined by the tilting angle 9, relative to the beamdirection Z. it is not necessary that the surface C be first rotatedabout the X-axis an angular amount D,, since the surface structure ofthe specimen object is almost always such that from the outset thesurfaces occupy a given angle relative to the plane defined by the Z-and X-axes.

One of the applicable ways of turning the face C to the positions C" orC, for taking the stereo pictures is as follows. The face C is rotatedabout the Z-axis into a second position C in such a manner that asubsequent tilting to the position C about the Y-axis by the stereoangle A does not cause a change in image brightness intensity for theface C. The face direction C" is determined by the fact that, upontilting the face C" one half of the stereo angle A012, it no longerpossesses a component in the X-axis direction. When displacing the faceC to C" and taking the electron-optical pictures, no stereo effect is atfirst produced since the face normals C and C do not change the anglerelative to the beam direction Z, i.e., their projections in the beamdirection remain unchanged. Consequently, their image intensity alsoremains unchanged. With this rotation, the other faces of the specimen Plikewise do not change their intensity.

The subsequent A0 tilting about the Y-axis, which transfers the face Cfrom the position C" to the position C does not change the imagebrightness, at least of the face C, because the directions C" and C ofthe face normals form the same angle a relative to the Z-axis as theface normal direction C.

The face positions C" and C differ from each other, with respect totilting about the Y-axis, by the stereo angle A0 and result in obtaininga pair of stereo pictures on which the face C has the same brightnessintensities respectively.

The second method according to the invention provides as a first stepthat an axis be moved in such a manner that it becomes identical with orparallel to the face normal direction on the chosen face of thespecimen. Thereafter the chosen face is rotated about this axis andbrought into two positions differing from each other by the stereo anglewhich is now dependent upon the angle defined by the central axis, i.e.,the electron-beam axis on the one hand, and the adjustable axis on theother hand. The latter angle can be computed or the positions can bedetermined experimentally.

The embodiments of apparatus according to the invention illustrated inH68. 2 and 3 are designed for performing the first-described methodaccording to the invention.

The device shown in FIG. 2 comprises three sliders S1, S2 and S3arranged one above the other and serving to impart translatorydisplacements to the specimen P shown situated on the central axis Z inthe path of the electron beam. The slider Si is used for the firsthorizontal translatory motion of the specimen, the slider S2 for thesecond horizontal specimen motion perpendicular to that of the slider81, and the slider S3 permits a vertical translatory movement of thespecimen in the direction of the electron beam which is along thecentral axis 2. Mounted on the slider 51 is a fixed axle MA which can beturned by means of a spur gear Zl. Seated on top of the axle MA is acardanic joint assembly of several gimbal members. One of these members,a U-shaped bracket member H1, is fastened to the axle MA and has itslateral legs SHl and 8H2 provided with inwardly directed journal pinsAl, A2. A frame R is secured to the ends of the pins Al and A2. Theframe is composed of four lateral parts 1, 2, 3, 4 of which the parts 1and 3 are connected with the pins Al and A2. Each of the lateral parts 2and 4 carries in its middle another axle pin A3 or A4 which protrudesinwardly in the plane defined by the frame R. Another U-shaped gimbalmember H2 has its lateral legs 5H3 and SH4 joined with the pins A3 andA4 respectively. The bottom B0 of member H2 carries the specimen supportPT on whose point the specimen P itself is fastened. The member HI, theframe R and the member H2 are angularly displaced 90 from each other soas to jointly form a cardanic or universal-joint suspension for thespecimen P. The electron-beam direction identical with the Z-axis passesthrough the specimen P and the axle MA. The X-axis for the angularrotation about the angle i (see FIG. 1) extends through the journal pinsA3 and A4; and the Y-axis extends through the pins Al and A2 ofthegimbal member H1.

Before a stereo picture of the specimen P can be taken, the specimen Pmust be brought into the focal point of the electron beam by applyingtranslatory displacements with the aid of the sliders S1, S2, S3. Fortaking a stereo picture with the imprecise known method, it suffices totilt the member H2 about the X-axis, i.e., about the journal pins A3 andA4. For taking stereo pictures by the method according to the invention,the I tilting is first used alone for adjusting a desired brightness ofthe image, and is not changed once this adjustment is made. Aftersuitable rotation of the specimen P about the beam direction (Z-axis)the stereo tilting is performed by tilting the specimen about theY-axis. The rotation about the Z-axis is transmitted to the specimen Pthrough the axle MA and the gimbal member Hl fastened to that axle. Thetilting about the Y-axis is effected by the journal pins Al and A2 whoserotation is transferred to the specimen P through the frame R and themember H2.

The apparatus shown in FIG. 3 resembles that of FIG. 2 in comprising twosliders S4 and S5 which are fastened one above the other and aredisplaceable at an angle of 90' relative to each other. An axle A5 ismounted on the slider S5 and rotatable by means of a spur gear Z2. Amounting structure W-shaped as an angle piece is fastened to the top endof the axle A5. The sliders S5 and S4 serve to shift the object P intothe center axis Z. A gimbal bracket member H3 is fastened by a pivot pinA6 to the upper end of the leg W1 of the angle piece W. The lateral legsSHS and 5H6 of the likewise U- shaped member H3 carry coaxial pins A7and A8 between which a U-shaped gimbal bracket H4 is attached. The pinsA7 and A8 engage the lateral legs SH7 and 8H8. The bottom of member H4carries on a further axle (not visible) a circular disc KS whose surfaceOB is perpendicular to the common axis of pins A7 and A8. A slider S6mounted on the disc surface carries another slider S7 displaceableperpendicularly to the sliding direction of slider S6. The displacementof slider S7 is along the common axis of pins A7 and A8. The specimencarrier PT with the specimen P is fastened on the sliding member SC ofthe slider S7.

The sliders S6 and S7 and the disc KS serve to place selected localitiesof the specimen P into the focal point of the electron beam Z withoutrequiring each time a new focusing of the electron beam onto thespecimen P situated parallel to the plane SC. The two sliders S4 and S5serve to bring the specimen P into the electron beam Z. The coarsedisplace ment of the specimen P in the direction of the central axis(coincident with the direction of the electron beam Z) is effected bymeans of the sliders S4 to S7.

For taking stereo pictures in accordance with the conventional imprecisemethod, a rotation of the specimen about the X-axis coincident with thecommon axis of the pins A7 and A8 may be used. This possibility ofrotation is also applicable for the purpose of the method according tothe invention, namely for improving the inclination of individualcrystal faces of the specimen P relative to the center axis Z and hencerelative to the electron beam direction. In this manner the brightnessof these faces can be varied. The tilting of the specimen about theZ-axis is effected by turning the angle piece W with the aid of the axleA5 fastened on the slider S5. The subsequent tilting about the Y-axis,important for taking stereo pictures, is effected with the aid of thebracket members H3 and the pivot pin A6.

We claim:

1. The method of producing electron-microscopic stereo images bysequentially taking pairs of stereoscopically coordinated individualpictures, which comprises exposing the object to be imaged to a beam ofelectrons whose direction defines a central axis, rotating the objectsurface area to be photographed about said central axis, then tiltingthe object an angular amount equal to the stereo angle about a secondaxis intersecting said central axis, the rotation about said centralaxis being in an angular amount at which the image brightness of saidarea is the same in the starting and end positions respectively of thetilting, and taking first and second pictures of the object when saidelectron-irradiated surface area is in said two positions respectively.

2. The method of producing electron-microscopic stereo images bysequentially taking pairs of stereoscopically coordinated individualpictures, which comprises exposing the objects to be imaged to a beam ofelectrons whose direction defines a central axis, adjusting anadjustable axis to be parallel to or in coincident relation with thenormal of the object surface area to be photographed, said adjustableaxis being noncoincident with said central axis, and rotating saidobject surface area about said adjustable axis an angular amount equalto the stereo angle, said angular amount corresponding to the angleformed between said central and said adjustable axes.

3. The method according to claim 1, which comprises rotationallyadjusting the object about a third axis for obtaining a surfacebrightness intensity, sufficient to permit said pictures to record astereoscopic image before said object surface area is rotated about saidcentral axis, said third axis passing through the intersection of saidcentral and second axes and extending transversely to each of saidlatter two axes.

4. The method according to claim 1, wherein said central axis and saidsecond axis are perpendicular to each other.

5. The method according to claim 4, which comprises mounting said objecton the intersection of said central and second axes.

6. The method according to claim 1, which comprises rotationallyadjusting the object about a third axis for obtaining a desired surfacebrightness intensity, sufficient to permit said pictures to record astereoscopic image before said object surface area is rotated about saidcentral axis.

7. ln apparatus for producing electron-microscopic stereo images bysequentially taking pairs of stereoscopically coordinated individualpictures having means for producing an electron beam in a directiondefining a central axis, a device for holding a specimen object on saidcentral axis, and means for photographically taking individual picturesof the electronilluminated object, the improvement according to whichsaid device comprises a cardanic joint assembly, of gimbal structures,having three cardanic journal axes of which one is coincident with saidcentral axis, said three axes having a common intersection on saidcentral axis, an object support mounted on said assembly near saidintersection for holding the object on said intersection, whereby saiddevice permits rotating any chosen surface area of the object about saidcentral axis and then tilting the object through the stereo angle aboutone of said other axes between two picture-taking positions in which thechosen area has substantially the same brightness, said gimbalstructures comprising a quadrangular frame at whose center point saidintersection is located, said frame having two coaxial pivot pinsprotruding from opposite frame sides, a first U-shaped gimbal member onwhose two legs said respective pivot pins are mounted to permit rotationof said frame about one of said cardanic journal axes, two further pivotpins protruding from the other two sides respectively of said frame anddefining another one of said journal axes, a second U- shaped gimbalmember fastened to said other pivot pins for rotation about said otherjournal axis, said object support being fastened to said second gimbalmember, a slider displaceable transversely of said central axis, an axlemounted on said slider and having an axis perpendicular to the sliderdisplacement direction, said axle being rotatable about its axis, saidfirst gimbal member being fastened to said axle to rotate togethertherewith, a second slider on which said first slider is displaceable,and a third slider on which said second slider is displaceable, thedisplacement directions of said three sliders extending at an angle of90 to each other, whereby respective translatory adjustments areapplicable to said object support relative to said central axis.

8. ln apparatus for producing electron-microscopic stereo images bysequentially taking pairs of stereoscopically coordinated individualpictures having means for producing an electron beam in a directiondefining a central axis, a device for holding a specimen object on saidcentral axis, and means for photographically taking individual picturesof the electronilluminated object, the improvement according to whichsaid device comprises a cardanic joint assembly of gimbal structures,having three cardanic journal axes of which one is coincident with saidcentral axis, said three axes having a common intersection on saidcentral axis, an object support mounted on said assembly near saidintersection for holding the object on said intersection, whereby saiddevice permits rotating any chosen surface area of the object about saidcentral axis and then tilting the object through the stereo angle aboutone of said other axes between two picture-taking positions in which thechosen area has substantially the same brightness, two slidersdisplaceable in respective directions perpendicular to each other, oneof said sliders carrying said object support and being mounted anddisplaceable upon the other slider, a rotatable circular disc structureto which said other slider is fixedly attached to be rotationallyadjustable together therewith, said rotatable discs being mounted onsaid cardanic assembly, said cardanic assembly comprising a firstU-shaped bracket on whose bottom said rotatable disc structure ismounted, a second U-shaped bracket having two leg portions withrespective coaxial pivot pins, said first bracket having two legportions connnected with said respective pivot pins to be rotatableabout their common axis, and an angle piece (W) and a pivot pinprotruding from one leg of said angle piece and having a pivot axiscoincident with one of said two cardanic journal axes other than saidcentral axis, said second bracket (H3) being journaled on said latterpivot pin to be rotatable about said one journal axis.

9. In apparatus for producing electron-microscopic stereo images bysequentially taking pairs of stereoscopically coordinated individualpictures having means for producing an electron beam in a directiondefining a central axis, a device for holding a specimen object on saidcentral axis, and means for photographically taking individual picturesof the electronilluminated object, the improvement according to whichsaid device comprises a cardanic joint assembly of gimbal structures,having three cardanic journal axes of which one is coincident with saidcentral axis, said three axes having a common intersection on saidcentral axis, an object support mounted on said assembly near saidintersection for holding the object on said intersection, whereby saiddevice permits rotating any chosen surface area of the object about saidcentral axis and then tilting the object through the stereo angle aboutone of said other axes between two picture-taking positions in which thechosen area has substantially the same brightness, two slidersdisplaceable in respective directions perpendicular to each other, oneof said sliders carrying said object support and being mounted anddisplaceable upon the other slider, a rotatable circular disc structureto which said other slider is fixedly attached to be rotationallyadjustable together therewith, said rotatable discs being mounted onsaid cardanic assembly, said cardanic assembly comprising a firstU-shaped bracket on whose bottom said rotatable disc structure ismounted, a second U-shaped bracket having two leg portions withrespective coaxial pivot pins, said first bracket having two legportions connected with said respective pivot pins to be rotatable abouttheir common axis, a mounting structure, and a pivot pin connected withsaid mounting structure and having an axis defining one of said cardanicjournal axes other than said central axis, said second bracket (H3)being journaled on said pivot pin for rotation about said one journalaxis.

10. Apparatus according to claim 9, comprising slider means displaceablein a direction transverse to said central axis, an axle (A5) mounted onsaid slider means and extending therefrom in a direction parallel tosaid central axis, said axle being adjustable by said slider means to aposition coaxial with said central axis, said mounting structure beingconnected to said axle so as to be rotatable about said central axis.

11. An apparatus according to claim 10, said slider means comprising atop slider (S) carrying said axle, and a bottom slider (S4) on whichsaid top slider is displaceable in a direction perpendicular to thedisplacement direction of said top slider, said bottom slider beingoperable to impart transla- 5 tory displacements to said axle (A5)relative to said central axis (Z).

1. The method of producing electron-microscopic stereo images bysequentially taking pairs of stereoscopically coordinated individualpictures, which comprises exposing the object to be imaged to a beam ofelectrons whose direction defines a central axis, rotating the objectsurface area to be photographed about said central axis, then tiltingthe object an angular amount equal to the stereo angle about a secondaxis intersecting said central axis, the rotation about said centralaxis being in an angular amount at which the image brightness of saidarea is the same in the starting and end positions respectively of thetilting, and taking first and second pictures of the object when saidelectron-irradiated surface area is in said two positions respectively.2. The method of producing electron-microscopic stereo images bysequentially taking pairs of stereoscopically coordinated individualpictures, which comprises exposing the objects to be imaged to a beam ofelectrons whose direction defines a central axis, adjusting anadjustable axis to be parallel to or in coincident relation with thenormal of the object surface area to be photographed, said adjustableaxis being noncoincident with said central axis, and rotating saidobject surface area about saiD adjustable axis an angular amount equalto the stereo angle, said angular amount corresponding to the angleformed between said central and said adjustable axes.
 3. The methodaccording to claim 1, which comprises rotationally adjusting the objectabout a third axis for obtaining a surface brightness intensity,sufficient to permit said pictures to record a stereoscopic image beforesaid object surface area is rotated about said central axis, said thirdaxis passing through the intersection of said central and second axesand extending transversely to each of said latter two axes.
 4. Themethod according to claim 1, wherein said central axis and said secondaxis are perpendicular to each other.
 5. The method according to claim4, which comprises mounting said object on the intersection of saidcentral and second axes.
 6. The method according to claim 1, whichcomprises rotationally adjusting the object about a third axis forobtaining a desired surface brightness intensity, sufficient to permitsaid pictures to record a stereoscopic image before said object surfacearea is rotated about said central axis.
 7. In apparatus for producingelectron-microscopic stereo images by sequentially taking pairs ofstereoscopically coordinated individual pictures having means forproducing an electron beam in a direction defining a central axis, adevice for holding a specimen object on said central axis, and means forphotographically taking individual pictures of the electron-illuminatedobject, the improvement according to which said device comprises acardanic joint assembly, of gimbal structures, having three cardanicjournal axes of which one is coincident with said central axis, saidthree axes having a common intersection on said central axis, an objectsupport mounted on said assembly near said intersection for holding theobject on said intersection, whereby said device permits rotating anychosen surface area of the object about said central axis and thentilting the object through the stereo angle about one of said other axesbetween two picture-taking positions in which the chosen area hassubstantially the same brightness, said gimbal structures comprising aquadrangular frame at whose center point said intersection is located,said frame having two coaxial pivot pins protruding from opposite framesides, a first U-shaped gimbal member on whose two legs said respectivepivot pins are mounted to permit rotation of said frame about one ofsaid cardanic journal axes, two further pivot pins protruding from theother two sides respectively of said frame and defining another one ofsaid journal axes, a second U-shaped gimbal member fastened to saidother pivot pins for rotation about said other journal axis, said objectsupport being fastened to said second gimbal member, a sliderdisplaceable transversely of said central axis, an axle mounted on saidslider and having an axis perpendicular to the slider displacementdirection, said axle being rotatable about its axis, said first gimbalmember being fastened to said axle to rotate together therewith, asecond slider on which said first slider is displaceable, and a thirdslider on which said second slider is displaceable, the displacementdirections of said three sliders extending at an angle of 90* to eachother, whereby respective translatory adjustments are applicable to saidobject support relative to said central axis.
 8. In apparatus forproducing electron-microscopic stereo images by sequentially takingpairs of stereoscopically coordinated individual pictures having meansfor producing an electron beam in a direction defining a central axis, adevice for holding a specimen object on said central axis, and means forphotographically taking individual pictures of the electron-illuminatedobject, the improvement according to which said device comprises acardanic joint assembly of gimbal structures, having three cardanicjournal axes of which one is coincident with said central axis, saidthrEe axes having a common intersection on said central axis, an objectsupport mounted on said assembly near said intersection for holding theobject on said intersection, whereby said device permits rotating anychosen surface area of the object about said central axis and thentilting the object through the stereo angle about one of said other axesbetween two picture-taking positions in which the chosen area hassubstantially the same brightness, two sliders displaceable inrespective directions perpendicular to each other, one of said sliderscarrying said object support and being mounted and displaceable upon theother slider, a rotatable circular disc structure to which said otherslider is fixedly attached to be rotationally adjustable togethertherewith, said rotatable discs being mounted on said cardanic assembly,said cardanic assembly comprising a first U-shaped bracket on whosebottom said rotatable disc structure is mounted, a second U-shapedbracket having two leg portions with respective coaxial pivot pins, saidfirst bracket having two leg portions connnected with said respectivepivot pins to be rotatable about their common axis, and an angle piece(W) and a pivot pin protruding from one leg of said angle piece andhaving a pivot axis coincident with one of said two cardanic journalaxes other than said central axis, said second bracket (H3) beingjournaled on said latter pivot pin to be rotatable about said onejournal axis.
 9. In apparatus for producing electron-microscopic stereoimages by sequentially taking pairs of stereoscopically coordinatedindividual pictures having means for producing an electron beam in adirection defining a central axis, a device for holding a specimenobject on said central axis, and means for photographically takingindividual pictures of the electron-illuminated object, the improvementaccording to which said device comprises a cardanic joint assembly ofgimbal structures, having three cardanic journal axes of which one iscoincident with said central axis, said three axes having a commonintersection on said central axis, an object support mounted on saidassembly near said intersection for holding the object on saidintersection, whereby said device permits rotating any chosen surfacearea of the object about said central axis and then tilting the objectthrough the stereo angle about one of said other axes between twopicture-taking positions in which the chosen area has substantially thesame brightness, two sliders displaceable in respective directionsperpendicular to each other, one of said sliders carrying said objectsupport and being mounted and displaceable upon the other slider, arotatable circular disc structure to which said other slider is fixedlyattached to be rotationally adjustable together therewith, saidrotatable discs being mounted on said cardanic assembly, said cardanicassembly comprising a first U-shaped bracket on whose bottom saidrotatable disc structure is mounted, a second U-shaped bracket havingtwo leg portions with respective coaxial pivot pins, said first brackethaving two leg portions connected with said respective pivot pins to berotatable about their common axis, a mounting structure, and a pivot pinconnected with said mounting structure and having an axis defining oneof said cardanic journal axes other than said central axis, said secondbracket (H3) being journaled on said pivot pin for rotation about saidone journal axis.
 10. Apparatus according to claim 9, comprising slidermeans displaceable in a direction transverse to said central axis, anaxle (A5) mounted on said slider means and extending therefrom in adirection parallel to said central axis, said axle being adjustable bysaid slider means to a position coaxial with said central axis, saidmounting structure being connected to said axle so as to be rotatableabout said central axis.
 11. An apparatus according to claim 10, saidslider means comprising a top slider (S5) carrying said axle, And abottom slider (S4) on which said top slider is displaceable in adirection perpendicular to the displacement direction of said topslider, said bottom slider being operable to impart translatorydisplacements to said axle (A5) relative to said central axis (Z).